Background
With Unity, I downloaded this asset (Unity Asset Store link) for a game I am doing. I decided to use the "Army1" soldier for my game, but I needed some animations.
After searching a bit on Google, I found that I needed Blender for doing them and to load the .fbx file on it for adding the rig necessary for models parts to move.
Blender work
When I loaded the model, it already had some bones on it, but those were for moving on a specific way, and did not allowed the model to move on more ways than that one pre-established.
Then, I deleted that rig and followed this (YouTube Rigify tutorial) to learn how to rig from scratch.
Problem
However, when I generated the rig (This is the .blend file), this error appeared:
Question
I have to say that I am very new to Blender, and a bit to Unity too. Any way I can solve this? Thanks in advance.